Polyphenylene ether engineering plastics are drawing attention because of their outstanding mechanical and thermal properties and self-extinguishing characteristics.
The flame-retardance of polyphenylene ether is not necessarily satisfactory. Moreover, polyphenylene ether has an extremely poor processability when used alone, and, in actual use, it is blended with styrene resin and other resins for the improvement of processability. (For blending with styrene resin, see U.S. Pat. No. 3,383,435.) This blending impairs the self-extinguishing properties of polyphenylene ether and the blended polyphenylene ether is more combustible than the straight polyphenylene ether. Thus, there is a demand for the improvement of polyphenylene ether in flame-retardance.
In order to overcome the above-mentioned drawback, polyphenylene ether is incorporated with an aromatic phosphate compound such as triphenyl phosphate as a flame retardant. Triphenyl phosphate imparts flame retardance, but, at the same time, it lowers the heat distortion temperature because it also works as a plasticizer. Therefore, at present there are no satisfactory methods for making polyphenylene ether compositions flame-retardant.
As a result of research on flame-retardance of polyphenylene ether, it has been found that polyphenylene ether can be made flame-retardant, without sacrificing its thermal properties, by adding thereto a bicyclophosphoric ester compound.